Method of manufacturing an HLA for an internal combustion engine

ABSTRACT

The present invention is related to a method of manufacturing HLA for an internal combustion engine, wherein the friction of valve drain system can be reduced approximately 30% due to the polishing effect as well as the initial engine tune-up resulted from an etching treatment additionally applied on the upper surface of the HLA already treated with high carbon carburization.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention is related to a method of manufacturing a hydraulic lash adjuster (HLA) for an internal combustion engine, and more particularly, to a method of manufacturing HLA for an internal combustion engine, wherein the friction of valve drain system can be reduced approximately 30% due to the polishing effect as well as the initial engine tune-up resulted from the etching treatment additionally applied on the upper surface of the HLA treated with high carbon carburization.

[0003] 2. Description of the Prior Art

[0004] A valve lifter in a combustion engine, actuated by a cam of a camshaft, shifts the rotational movement of the cam into a reciprocal movement and thereby transmits the power of an internal combustion engine into the valve through a rocker arm of a push rod. Further, the valve lifter is generally provided with a hydraulic lash adjuster (hereinafter referred to as HLA) so that the valve lifter can be actuated without a gap between valve and cam regardless of the operating temperature. FIG. 1 shows a structure of an HLA. The HLA includes a lash adjuster 10 that is in contact with a cam 19 of a camshaft 18, and the interior 12 of the main lash adjuster 10 is provided with a lash adjuster piston, a ball valve, a gap adjusting spring and the like. The main lash adjuster 10 (hereinafter referred to as HLA) is biased to the upward direction by a spring 16 installed on a valve 14 and thus it can prevent the generation of a gap while still maintaining the contact with the cam 19 at the same time. FIG. 2 shows the process of manufacturing an HLA according to the conventional method. According to the conventional method, a carbon steel such as SCM 415H is first fixed onto a drawer (step S10) and then placed into a drawing process to generate a proper diameter (step S12). Once a selected material is passed through a drawing process, it is then placed under a cold honing process followed by a carburization (step S16). Finally, the carburized material is placed on a finishing process and the production of the HLA comes to a completion (step S18).

SUMMARY OF THE INVENTION

[0005] HLAs manufactured according to the conventional methods, although not showing any problems with respect to wear resistance, have not been considered advantageous in that the friction torque is increased when they are in contact with camshaft during the course of rolling and sliding because it results in the increase in friction in a valve drain system thus decreasing the fuel efficiency of an automobile. Unlike other mechanical lash adjusters, however, the surface pressure of the HLA is not high enough because the HLA is under a hydraulic control and thus the tuning of the upper surface of HLA is hardly accomplished.

[0006] To solve these problems, the present invention applies an additional etching treatment to the upper surface of the HLA, which is already gone through with a series of steps of drawing, cold honing, and high carbon carburizing, thus enabling to reduce the friction in a valve drain system by approximately 30% as well as resulting in an initial engine tune-up and a polishing effect on the upper surface of the HLA thus manufacturing the HLA of an internal combustion engine which can increase the fuel efficiency by approximately 2-3%.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007]FIG. 1 shows a schematic cross-sectional view of a general HLA of an internal combustion engine of an automobile.

[0008]FIG. 2 is a flow chart that shows the process of manufacturing the HLA according to the conventional method.

[0009]FIG. 3 is a flow chart that shows the process of manufacturing the HLA according to the present invention.

[0010] [Code Explanation of Major Parts]

[0011]10: hydraulic lash adjuster

[0012]14: valve

[0013]18: camshaft

[0014]19: cam

DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention is related to a method of manufacturing an HLA of an internal combustion engine.

[0016] The present invention, presented as a way to solve the above-mentioned problems of the conventional HLAs, is characterized by comprising a drawing process to generate a given material such as MAC 14 to have an appropriate diameter; a cold honing process; a high carbon carburizing process to improve wear resistance, a finishing process to finish up the carburized surface; and an etching process using NITAL for a predetermined period of time.

[0017] The manufacturing method of the HLA according to the present invention can be explained in more detail as made reference to FIG. 3 as described hereunder wherein the reference numbers in FIG. 3 correspond to the same numbers in FIG. 1.

[0018]FIG. 3 is a flow chart that shows the process of manufacturing an HLA according to the present invention.

[0019] As shown in FIG. 3, the example of the present invention employed a method to additionally applying an etching step after a finishing process to HLA an already treated with high carbon carburization. That is, a material such as MAC14 is fixed on a drawer (Step S20), placed onto a drawing process (step S24), placed in a cold honing process, treated with high carbon carburization to improve wear resistance, and then finally placed on a finishing process to finish up the carburized surface (Step S28).

[0020] The above steps (S20-S28) are disclosed in Korean Unexamined Patent Publication No. 2000-0037732 by the same applicant of the present invention.

[0021] This reference relates to a high carbon carburizing method to improve pitting resistance, wear resistance and friction resistance of a steel. More particularly, this reference relates to a high carbon carburizing method, wherein low carbon steel is started to carburize in the presence of carbon concentration exceeding that of Acm at a temperature higher than Ac1 of a Fe-C state diagram and this process is continued while increasing its temperature till it reaches an austenite state and eventually forms minute carbides within a carburized layer thus resulting in the improvement of pitting resistance, wear resistance and friction resistance of a steel.

[0022] This kind of high carbon carburizing method can be applied to parts such as a mechanical lash adjuster of an internal combustion engine of an automobile, a valve lifter, a connecting rod, a bearing, a drive shaft, a high load gear and the like.

[0023] After the high carbon carburization, the surface treated with a finishing process then goes through an etching step using NITAL for a predetermined time (approximately 50 sec). The method of etching using NITAL is disclosed in U.S. Pat. No. 5,972,128. This reference clearly discloses the method of etching for tins and piston rings. FIG. 2 shows an enlarged picture of a tin structure processed with etching by NITAL. Meanwhile, FIG. 1 shows an enlarged picture of a tin structure not processed with etching.

[0024] A series of experiments were carried out by the present inventors to figure out the effect of an HLA installed in an automobile, which is treated with etching after high carbon carburization, as compared to those of the conventional carburized HLAs. The results showed that the HLA manufactured according to the present invention has a relatively lower friction by approximately 30% as compared to those of conventional carburized HLAs, and this lower friction rate is equivalent to that of tin. Moreover, the HLA manufactured according to the present invention also showed an excellent fuel efficiency which is comparable to that of the upper surface of XD taper lash adjuster.

[0025] The HLAs not treated with etching after high carbon carburization did not show any marked improvement in friction but rather negligible as compared to those of conventional HLAs and this appears because the upper surface of the HLA was not polished at all thus not enabling to reduce friction.

[0026] The HLAs treated with etching after high carbon carburization have a relatively higher friction torque before break-in as compared to those of tins by approximately 10%, however, 3 hr of break-in resulted in having the similar friction torque to those of tins and the friction torque remained constant after 800 rpm/10 h and 3,000 rpm/10 h.

[0027] Consequently, the HLAs of the present invention, being additionally treated with etching after high carbon carburization, showed a decrease in friction and an increase in fuel efficiency, and the reduction of break-in time resulted in the increase in etching period from 50 sec to 100 sec.

[0028] As mentioned above, the HLA manufactured according to the present invention with additional etching treatment after high carbon carburization enables to have an initial engine tune-up and a polishing effect on the upper surface of the HLA thus reducing the friction in a valve drain system by approximately 30% and subsequently increases the fuel efficiency of an automobile by approximately 2-3%. 

what is claimed is:
 1. A method of manufacturing an HLA of an internal combustion engine characterized by comprising: (a) a drawing process to generate a given material such as MAC 14 to have an appropriate diameter; (b) a cold honing process; (c) a high carbon carburizing process to improve wear resistance; (d) a finishing process to finish up the carburized surface; (e) and an etching process using NITAL for a predetermined period of time.
 2. In claim 1, said finishing surface is treated with NITAL for 50 sec. 